Modern wireless communications technology uses radio frequencies (RF) to transmit information. A variety of frequencies are available for such transmission, depending on the complexity of the information being transmitted, such as text versus multi-channel video. A variety of standards, including for example Bluetooth and WiFi, have been developed for mid- to high-range data rates for voice, PC LANs, video and the like. In contrast, the only standard currently in place for remote control and sensor applications is Zigbee. Sensor and control networks do not require high bandwidth, but do require low latency and low power consumption. ZigBee provides for a general-purpose, inexpensive self-organising mesh network that is designed to use small amounts of power.
A mesh network is an example of one of a number of protocols that take advantage of peer-to-peer style networking in order to reduce complexity and power usage of wireless devices, while still providing the network with considerable overall reach. In peer-to-peer style networks, each node in the network has the capacity to communicate with any other node in the network independently of a central server or router. This network design philosophy, combined with low power, high frequency radio transmissions can be used to build a distributed intelligent network where information is routed through the network on an ad hoc basis and that organises itself to pass data from one node to the next until it reaches the destination node. Nodes act as repeaters to transmit data from nearby nodes to nodes that are too far away to reach, resulting in a network that can span large distances, especially over rough or difficult terrain. This results in a network that is extremely robust and which can adapt easily to changes in the network, such as the introduction of new nodes. Examples of peer-to-peer style network topologies include mesh, ad hoc mesh, mobile mesh, star, cluster tree and various hybrids of these.
Regulation of the radio spectrum for information requires users wishing to broadcast in the higher bandwidth frequencies to pay licensing fees. These license costs add to the creation, scalability and maintenance costs of any system using wireless communication methods. To address this, wireless devices have been developed to use frequency bands that do not require licenses, such as the unlicensed Industrial, Scientific and Medical (ISM) frequency bands. These frequency bands are, however, very narrow, which limits the amount of information that can be transmitted quickly. ZigBee uses the IEEE 802.15.4 Low-Rate Wireless Personal Area Network (WPAN) standard to describe its lower protocol layers (the physical layer PHY, and the medium access control MAC portion of the data link layer or DLL). This standard specifies operation in the unlicensed 2.4 GHz, 915 MHz and 868 MHz ISM bands. Zigbee products use conventional Direct Sequence Spread Spectrum (DSSS) in the 868 and 915 MHz bands, and an orthogonal signalling scheme that transmits four bits per symbol in the 2.4 GHz band. Although each node in a network employing Zigbee standard products can act as a repeater to transmit data multihop fashion to distant nodes, the transmission range of each node in a Zigbee-based network is typically between 10 and 75 metres (approximately 33 to 250 feet). Although it may be possible to extend the transmission range of a Zigbee device up to 500 m in a favourable environment, the average transmission range is about 50 m, this limiting the inter-node distance in the network to about 50 m.
A wide variety of industrial, medical, agricultural, consumer and military applications can benefit from some form of sensor or control network, such as security systems, monitoring digital precision instruments on the factory floor, monitoring shipments through a supply chain, monitoring and reporting seismic activity, medical implants, irrigation management, and the like.
A number of control systems have been developed for automatic irrigation systems that are used for landscape and agricultural maintenance. Automatic irrigation systems generally comprise a network of under and above-ground pipes and pumps that convey water to desired areas, and water valves and pumps that are used to control the flow of irrigation water through a variety of water dispensing devices, including rotors and sprinklers. Rotors are typically enclosed in a protective housing, and a rotating nozzle pops up from the top of the housing during desired irrigation times and irrigates by throwing a jet or spray of water that is rotated about a generally vertical axis. Each rotor, when not in use, sits in its protective housing such that the top cover of the rotor is generally flush with the surrounding ground. Rotors are typically actuated by electric solenoid-controlled valves, which are in turn generally controlled via wires that are run from a controller to each solenoid valve and a pump that controls the flow of water to a sprinkler or group of sprinklers. Control wires to the valves, pumps and rotors are typically buried below ground, often in the same trenches used to run supply pipes to the valves. Control systems vary from simple multi-station timers to complex computer-based controllers.
Hard wired systems such as these are, however, expensive to install, are not easily scalable and are extremely vulnerable to lightning strikes or damage to the control wires. Damage to buried control wires can be difficult to trace and repair, increasing the cost of such systems. As a result, attempts have been made to develop wireless and quasi-wireless system using two-way paging, cellular and GPS technologies as well as primary wireless radio frequency communication platforms. Such communication systems are, however, power intensive, and the signals can be disrupted by obstacles such as buildings, metal structures, hills, cloud cover or even dense foliage. Most of these systems employ one-way communications to change or modify a pre-programmed irrigation schedule stored in the control mechanism. Pre-programmed irrigation schedules, however, are unable to adapt to environmental changes such as precipitation or microclimates, which can result in water being wasted in irrigating at times when irrigation is not required.
A number of wireless or quasi-wireless controls for irrigation systems have been described. U.S. Pat. No. 6,782,310, for example, describes a network of irrigation control devices in wireless communication with a main controller. The main controller uses commercial paging or public broadcast network signals to update watering schedules stored in the memory of the irrigation control devices.
U.S. patent application Ser. No. 10/732,911 describes an automated landscape irrigation control system which uses communication techniques such as wireless telephone transmissions to collect environmental information and derive irrigation schedules which are then sent to irrigation control units. The irrigation control units in turn control a plurality of irrigation stations such as valves or sprinklers.
U.S. Pat. No. 6,600,971 describes a system for operating a distributed control network for irrigation management. The system incorporates a peer-to-peer network of satellite irrigation controllers which can be in communication with a central computer. The network is connected by a communication bus which includes a radio modem but can be controlled through wireless transmissions. Each irrigation controller controls solenoid operated sprinkler valves and optionally sensors. The system is a quasi-wireless system in which the satellite irrigation controllers have wireless capability to be controlled from a central computer or hand held device, but the satellite irrigation controllers need to be hard-wired to the solenoid operated sprinkler valves by field wiring. Thus, although control wiring from the central computer to the satellite station could be eliminated, the system would still require the laying of control wire underground from the satellite irrigation controllers to the solenoid operated sprinkler valves. The system operates on AC power so each satellite irrigation controller requires a 120 volt power supply, which requires 120 volt wiring to the satellite irrigation controller from a generator and hard wiring from the satellite irrigation controller to each sprinkler valve.
U.S. patent application Ser. Nos. 10/692,645 (2005/0090936), 10/692,476 (2004/0100394), 10/692,518 (2004/0090345), 10/692,519 (2004/0090329) and 10/693,017 (2004/0083833) all describe a method for wireless environmental monitoring and control utilising a distributed wireless network of independent sensor and actuator nodes that communicate with each other to transmit sensor data or a command to control the sensor or actuator. The system is designed to be self-operating without the need for a central controller and thus requires that the nodes in the system be relatively complex and able to make decisions independently. These patent applications also describe a multi-hop wireless sensor irrigation control system configured into a plurality of irrigation zones, each comprising a plurality of sensor nodes, actuator nodes and repeater nodes. Control of the system requires a large number of independent sensor and actuator nodes, which in combination with the multi-hop transmission of information signals, results in a large amount of RF traffic within the system. The amount of traffic is further increased when independent repeater nodes are used.
The above patent applications also describe a wireless control system that can be used as an add-on to a pre-existing hard-wired irrigation system. The sensor system provides a moisture control override mechanism to an existing wired irrigation system that schedule irrigation cycles and times. The system of wireless moisture sensor nodes communicate moisture levels to an actuator node that is attached to the common power line of a two-wire power supply system and provides the ability to control and/or override the predetermined irrigation schedule that is controlled by hard-wire from the main terminal.
U.S. Pat. No. 5,813,606 describes a plurality of moisture sensors in wireless communication with a control unit that activates an irrigation system in response to signals from the moisture sensors.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.